Geneticists pen new tales of human history with the ink of ancient DNA

Posted on: 02 February 2017

Geneticists from Trinity College Dublin have helped to pen new tales of human history after they sequenced DNA from human remains found in Russia, Latvia and Ukraine. Working with colleagues in Cambridge, UCD, Riga and elsewhere, their analyses have shed new and surprising light on the evolution of our species.

By analysing the remains interred in Russia some 8,000 years ago, the scientists unlocked the secret that certain modern East Asian populations still closely resemble their hunter-gatherer ancestors in terms of their genetic structure.

The findings from this portion of their work, reported in Science Advances, thus indicate that there was no major migratory interruption or “population turnover” for well over seven millennia. Consequently, some contemporary ethnic groups share a remarkable genetic similarity to Stone Age hunters that once roamed the same region.     

The high “genetic continuity” in East Asia is in stark contrast to most of Western Europe, where sustained migrations of early farmers from the Levant overwhelmed hunter-gatherer populations. This was followed by a wave of horse riders from Central Asia during the Bronze Age. These events were likely driven by the success of emerging technologies such as agriculture and metallurgy.

Despite being separated by a vast expanse of history, this has allowed an exceptional genetic proximity between the Ulchi people of the Amur Basin, near where Russia borders China and North Korea, and the ancient hunter-gatherers laid to rest in a cave close to the Ulchi’s native land.

The researchers suggest that the sheer scale of East Asia and dramatic variations in its climate may have prevented the sweeping influence of Neolithic agriculture and the accompanying migrations that replaced hunter-gatherers across much of Europe. They note that the Ulchi retained their hunter-fisher-gatherer lifestyle until recent times.

The Trinity team was responsible for extracting DNA from the remains, which were found in a cave known as Devil’s Gate. Situated in a mountainous area close to the far eastern coast of Russia that faces northern Japan, the cave was first excavated by a soviet team in 1973.

Along with hundreds of stone and bone tools, the carbonised wood of a former dwelling, and woven wild grass that is one of the earliest examples of a textile, were the incomplete bodies of five humans.

“We attempted to extract DNA from all five of these individuals but found that only in the skulls of two females — one in her early twenties and the other close to fifty – was there enough DNA for us to explore the genetics of these ancient people,” said Research Fellow, Eppie Jones. 

If ancient DNA can be found in sufficiently preserved remains, sequencing it involves sifting through the contamination of millennia. The site itself dates back over 9,000 years, but the two women are estimated to have died around 7,700 years ago.

Researchers were able to glean the most from the middle-aged woman. Her DNA revealed she likely had brown eyes and thick, straight hair. She almost certainly lacked the ability to tolerate lactose, but was unlikely to have suffered from ‘alcohol flush’: the skin reaction to alcohol now common across East Asia.

In the second portion of their work, which is described in Current Biology, the Trinity team turned their attention to ancient DNA obtained from remains from Latvia and Ukraine that were between 5,000 and 8,000 years old.

Two key new narratives emerged from this research.

Firstly, these Baltic hunter-gatherers were not swamped by migrations of early agriculturalists from the Middle East, as was the case for the rest of Central and Western Europe. Instead, they probably acquired knowledge of farming and ceramics by sharing cultures and ideas — rather than genes — with outside communities. 

And secondly, one of the samples suggested a genetic link to the peoples of the Pontic Steppe, in the east. The timing (5-7,000 years ago) fits with previous research estimating the earliest Slavic languages.

Eppie Jones, lead author of this study, said: “There are two major theories on the spread of Indo-European languages, the most widely spoken language family in the world. One is that they came from the Anatolia with the agriculturalists; another that they developed in the Steppes and spread at the start of the Bronze Age.”

“That we saw no farmer-related genetic input, yet we do find this Steppe-related component, suggests that at least the Balto-Slavic branch of the Indo-European language family originated in the Steppe grasslands of the East, which would bring later migrations of Bronze Age horse riders.”

Senior author of the study, Professor Daniel Bradley of Trinity College Dublin, said: “Our findings feed into debates around the ‘Neolithic package,’ — the cluster of technologies such as domesticated livestock, cultivated cereals and ceramics, which revolutionised human existence across Europe during the late Stone Age.”

“Advances in ancient DNA work have revealed that this ‘package’ was spread through Central and Western Europe by migration and interbreeding: the Levant and later Anatolian farmers mixing with and essentially replacing the hunter-gatherers.”

“But the new work suggests migration was not a ‘universal driver’ across Europe for this way of life. In the Baltic region, archaeology shows that the technologies of the ‘package’ did develop — albeit less rapidly – even though our analyses show that the genetics of these populations remained the same as those of the hunter-gatherers throughout the Neolithic.”